Thorpe-Ingold effect

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The Thorpe-Ingold effect or gem-dimethyl effect, or angle compression is an effect observed in organic chemistry where increasing the size of two substituents on a tetrahedral center leads to enhanced reactions between parts of the other two substituents. The effect was first reported by Beesley, Thorpe and Ingold in 1916 as part of a study of cyclization reactions.

A common application of this effect is addition of a quaternary carbon (e.g., a gem-dimethyl group) in an alkyl chain to increase the reaction rate and/or equilibrium constant of cyclization reactions. An example is this is an olefin metathesis reaction:[1]

File:Tiemethathesis.PNG

One proposed explanation for this effect is that the increased size of the substituents increases the angle between them. As a result, the angle between the other two substituents decreases. By moving them closer together, reactions between them are accelerated.

File:Thorpeingoldeffect.PNG

References

  1. Fürstner, A. "A Concise Total Synthesis of Dactylol via Ring Closing Metathesis". J. Org. Chem. 61 (25): 8746–8749. doi:10.1021/jo961600c. Unknown parameter |coauthors= ignored (help)

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